Comparative Catalytic Activity of Graphene Imperfections in Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is the key operating process that determines the efficiency of energy storage and conversion devices; however, due to sluggish kinetics, it requires a catalyst. In recent years, the trial-and-error approach for the catalyst development has been gradually replaced by the rational design based on theoretical predictions of catalytic activity, which includes the use of so-called descriptors, i.e., certain properties of the catalyst that correlate with the electrocatalytic activity of the material and can be evaluated relatively easily. To assess the applicability of different ORR activity descriptors to a variety of possible catalytic centers of doped graphene (impurity atoms, vacancies, and their combination), here, we consider different graphene imperfections by treating them within the same formalism using the following known descriptors: spin density at the impurity center, molecular orbital descriptor E_diff, charge redistribution in graphene caused by the imperfection, and charge redistribution under electrode polarization. To link the catalytic activity to the electronic properties of graphene, we calculated the partial electron density of states (PDOS) related to the reaction site at the Fermi level and local density of states for the reaction center, which are directly related to the electron transfer rate during the ORR. We found their reasonable correlation with PDOS. This fact indicates that descriptors based on the quantum theory are generally the most promising ones for reactivity predictions.